Wafers used as substrates of semiconductor devices are produced by slicing ingots of silicon, compound semiconductor, or the like and conducting a surface grinding (lapping) process, an etching process, and mirror-polishing (polishing) process, followed by final cleansing. Herein, such objects, including the ingots, to be cut by the wire saw device are called “workpieces.”
Generally, a wire saw device used to slice a workpiece into wafers includes at least one wire provided tightly to be capable of travelling in a direction crossing the workpiece to be cut, a workpiece holder configured to hold the workpiece and to move the workpiece relative to the wire, and slurry suppliers configured to supply slurry to cut the workpiece from the upstream side in a travelling direction of the wire. In the wire saw device, the workpiece may be sliced into wafers by pressing the workpiece held by the workpiece holder against the fast-travelling wire while slurry is supplied from the slurry supplier to the wire.
In an early stage of the workpiece cutting process, a portion of slurry supplied from the slurry supplier to the wire is entrained into a cut of the workpiece to contribute to the cutting, while the remaining portion of slurry is dropped below the wire without contributing to the cutting. From the mid-stage and onward of the workpiece cutting process, the portion of slurry that used to be dropped without contributing to the cutting in the early stage starts to be scattered upward along an inclination of the workpiece and splash on a workpiece surface and the workpiece holder since the workpiece has a cylindrical shape.
The slurry splashing on the workpiece and the workpiece holder poses a problem that the excessively cooled workpiece and workpiece holder shrink, resulting in deterioration in cutting surface waviness index, such as nanotopography and Warp, of the sliced workpiece. An increase in cutting surface waviness component is difficult to correct perfectly in the subsequent lapping or polishing process and accordingly, significantly affects the shape and quality of the wafers as final products.
As a technology to solve the above problem, Patent Literature 1 proposes a wire saw device including slurry collectors configured to collect the slurry scattered upward due to contact with the workpiece. FIG. 1 illustrates the wire saw device proposed in Patent Literature 1. In the illustrated wire saw device 100, reference numeral 11 denotes the wire, reference numeral 12 denotes the workpiece holder, reference numeral 13 denotes the slurry supplier, and reference numeral W denotes the workpiece. The slurry collectors 14 are provided in a portion of the workpiece holder 12 that are located far away from the wire 11 and above the workpiece W to avoid contact between the slurry collector 14 and the wire 11 etc.